kallentu

class Reader<out T> {
  // Compile-time error: Can't use 'out' type variable 'T' in an 'in' position.
  void write(T x) => print(x);

  // OK
  T read() => null;
}

class Writer<in T> {
  // Compile-time error: Can't use 'in' type variable 'T' in an 'out' position

kallentu

// Add a contravariant variance modifier
class Writer<in T> {  
  void write(T x) => print(x);
}

main() {
  // Compile-time error: The constructor returns type 'Writer<int>'
  // that isn't of expected type 'Writer<Object>'.
  Writer<Object> objectWriter = Writer<int>();
}

kallentu

class Writer<T> {
  void write(T x) => print(x);
}

main() {
  Writer<Object> objectWriter = Writer<int>();
  objectWriter.write(“I’m a string!”);
}

kallentu

class MyContravariantClass<in T> {}
mixin MyInvariantMixin<inout T> {}

kallentu

class ReaderWriter<T> {
  void write(T x) => print(x);
  T read() => null;
}

main() {
  ReaderWriter<int> intRW = ReaderWriter<Object>();
  
  // Any object can be returned, not just integers. This is unsafe.
  intRW.read(); 

kallentu

main() {
  // ...
  // Runtime error!
  // Unhandled exception: type 'String' is not a subtype of type 'int' of 'x'
  objectWriter.write("Hello world!");
}

kallentu

class Writer<T> {
  void write(T x) => print(x);
}

main() {
  Writer<Object> objectWriter = Writer<int>();
  objectWriter.write(2);
}

kallentu

main() {
  Iterable<Object> objectIterable = <int>[1, 2, 3];
}

kallentu

<link href='https://fonts.googleapis.com/css?family=Pontano+Sans' rel='stylesheet' type='text/css'>
<div class="container jumbotron">
  <div class="text-center col-md-12">
    <h1>Monty Oum</h1>
    <h3><em>Influential Animator and DDR Master</em></h3>
    <img class="monty-image" alt="Monty" src="https://upload.wikimedia.org/wikipedia/commons/c/c2/Monty_Oum_at_PAX_2013.jpg">
  </div>
  <p class= "text-justify col-xs-12 col-md-8 col-md-offset-2 col-sm-10 col-sm-offset-3">Monty Oum was a self-taught animator who worked at Rooster Teeth, making animations for <em>Red Vs. Blue</em>. Afterwards, he created the animated series <em>RWBY</em>. He was occasionally on the RoosterTeeth podcasts and RTLife videos. Visit his <a href="http://roosterteeth.wikia.com/wiki/Monty_Oum">RTWikia</a> for more information.</p>
  <div class="text-center col-xs-12 col-md-8 col-md-offset-2 col-sm-10 col-sm-offset-3">
    <h3>Filmography</h3>